Electric machines have a casing that houses a stator and a rotor. The casing contains a gas (for example hydrogen) that is used as a cooling gas for the stator and rotor.
The gas can contain humidity that must be removed, because it can cause corrosion and electric flashover.
In order to remove humidity from the gas, dryers are provided; dryers are usually outside of the casing and are connected to the casing via pipes.
A type of dryer often used is the so called condensation dryer.
Condensation dryers have a heat exchanger; warm and potentially humid gas coming from the electric machine enters the heat exchanger at one side thereof and cooled gas exits at the other side thereof.
During operation the heat exchanger cools the gas causing humidity condensation; water drops separate from the gas and are collected inside the heat exchanger. In addition, a drop separator may be connected downstream of the heat exchanger in order to collect remaining drops.
A float valve is located below the heat exchanger (or drop separator); the float valve is connected to the heat exchanger (or drop separator) via a water line and a venting line. Water thus moves down into the float valve via the water line and, at the same time, gas moves up from the float valve into the heat exchanger (or drop separator) via the venting line (otherwise water could not properly enter the float valve).
From the float valve water is discharged.
In case of troubles at the float valve, such that the float valve remains open and does not close anymore, the gas could be inadvertently discharged from the casing via the heat exchanger, drop separation, water and gas line and float valve.
This must be avoided, because the gas pressure inside the electric machine would drop, reducing the cooling capabilities of the gas and eventually cause a trip of the electric machine, e.g. via a pressure or temperature supervision device.